The invention relates to fabricating ceramic matrix composite (CMC) material parts.
CMCs are formed of refractory fiber reinforcement made of carbon or ceramic fibers, together with a ceramic matrix. The fabrication of CMC parts usually comprises making a fiber structure or preform that is to constitute the fiber reinforcement of the composite material, and densifying the preform with the ceramic material of the matrix.
CMCs present mechanical properties that may be suitable for constituting structural parts and they present the ability to conserve these properties at high temperatures in an oxidizing environment.
Nevertheless, whether during fabrication or subsequently on exposure to thermomechanical stresses, CMCs are subjected to the ceramic material cracking. It is desirable to avoid cracks propagating, and in particular propagating as far as the fibers since that might break the fibers, thereby weakening the mechanical properties of the composite material. It is known to coat the fibers in a fiber-matrix interphase coating that has the ability to deflect cracks propagating in the matrix and reaching the interphase coating, while also ensuring bonding between the fibers and the matrix suitable for conferring the desired mechanical properties on the composite material. Crack-deflecting interphase coatings are typically made of pyrolytic carbon (PyC) or of boron nitride (BN), as described in particular in U.S. Pat. No. 4,752,503. It is also know to interpose PyC or BN crack-deflecting continuous phases between ceramic matrix phases, as described in U.S. Pat. No. 5,079,039.
It is also desirable that the appearance of cracks should not make it easier for an oxidizing atmosphere to have access to the core of the material. Such access could have damaging consequences on the fibers, if they are carbon fibers, and also on the interphase coating. It is known for this purpose to provide one or more healing phases within the matrix, i.e. phases capable of healing the cracks that appear in the matrix. Such healing matrix phases are typically made of compounds, in particular boron compounds, that are suitable in the presence of oxygen for forming vitreous compositions that take on a pasty state and that perform a healing action within a certain temperature range. Amongst others, reference can be made to U.S. Pat. No. 5,965,266 that describes the formation of continuous self-healing phases within the matrix.
In the above-mentioned documents, making interphases or matrix phases having crack-deflecting properties or healing properties relies on the chemical vapor infiltration (CVI) technique. That technique is well understood, but it requires very long durations and is therefore quite expensive. Furthermore, using CVI to form matrix phases of different kinds requires changes to the nature to the reaction gas used and to the parameters of the CVI process (temperature, pressure, gas flow rate, . . . ).
U.S. Pat. No. 5,094,901 proposes introducing fillers suitable for producing a healing effect into the fiber structure before making a fiber-matrix interphase by CVI and before forming a ceramic matrix. The fillers are typically one or more materials capable, in the presence of oxygen, of forming B2O3 and possibly SiO2. Powders of B4C, SiB6, or BN can be used, which powders are introduced into the fiber structure in the dispersed state in a resin solution dissolved in a solvent, with the fiber structure then being impregnated with the resulting suspension. The resin is carbonized prior to forming the interphase. It should be observed that the powders constituting precursors for B2O3 and possibly SiO2 are put into place solely on the fibers of the reinforcing fiber structure and the fiber-matrix interphase, with the matrix being formed subsequently by CVI.
In U.S. Pat. No. 5,962,103, a method of obtaining a composite having an SiC—Si ceramic matrix comprises forming a fiber-matrix interphase coating on the fibers of the fiber structure, introducing C or SiC or C+SiC and a boron compound in powder form, and infiltrating molten silicon. A composite material is thus obtained that has a matrix with self-healing properties.